Inkjet printhead having nozzle plate supported by encapsulated photoresist

ABSTRACT

An inkjet printhead is provided. The printhead comprises a plurality of nozzles formed on a substrate, and at least one nozzle plate spaced apart from the substrate. The nozzle plate is supported, at least partially, by encapsulated photoresist. Hence, the nozzle plate has improved robustness.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a Continuation in Part Application of U.S. Ser. No. 10/728,970filed Dec. 8, 2003, now abandoned, which is a Continuation In PartApplication of U.S. Ser. No. 10/160,273 filed Jun. 4, 2002, now issuedas U.S. Pat. No. 6,746,105, which is a Continuation Application of U.S.Ser. No. 09/112,767 filed Jul. 10, 1998, now issued as U.S. Pat. No.6,416,167, the entire contents of which are herein incorporated byreference.

The following Australian provisional patent applications/granted patentsare hereby incorporated by cross-reference. For the purposes of locationand identification, US patent applications identified by their U.S.patent application serial numbers (USSN)/granted Nos. are listedalongside the Australian applications from which the U.S. patentapplications claim the right of priority.

Cross-Referenced Australian US Patent/Patent Application ProvisionalPatent (Claiming Right of Priority from Application No. AustralianProvisional Application) PO7991 6750901 PO8505 6476863 PO7988 6788336PO9395 6322181 PO8017 6597817 PO8014 6227648 PO8025 6727948 PO80326690419 PO7999 6727951 PO8030 6196541 PO7997 6195150 PO7979 6362868PO7978 8631681 PO7982 6431669 PO7989 6362869 PO8019 6472052 PO79806356715 PO8018 6894694 PO7938 6636216 PO8016 6366693 PO8024 6329990PO7939 6459495 PO8501 6137500 PO8500 6690416 PO7987 7050143 PO80226398328 PO8497 7110024 PO8020 6431704 PO8504 6879341 PO8000 6415054PO7934 6665454 PO7990 6542645 PO8499 6486886 PO8502 6381361 PO79816317192 PO7986 6850274 PO7983 09/113054 PO8026 6646757 PO8028 6624848PO9394 6357135 PO9397 6271931 PO9398 6353772 PO9399 6106147 PO94006665008 PO9401 6304291 PO9403 6305770 PO9405 6289262 PP0959 6315200PP1397 6217165 PP2370 6786420 PO8003 6350023 PO8005 6318849 PO80666227652 PO8072 6213588 PO8040 6213589 PO8071 6231163 PO8047 6247795PO8035 6394581 PO8044 6244691 PO8063 6257704 PO8057 6416168 PO80566220694 PO8069 6257705 PO8049 6247794 PO8036 6234610 PO8048 6247793PO8070 6264306 PO8067 6241342 PO8001 6247792 PO8038 6264307 PO80336254220 PO8002 6234611 PO8068 6302528 PO8062 6283582 PO8034 6239821PO8039 6338547 PO8041 6247796 PO8004 6557977 PO8037 6390603 PO80436362843 PO8042 6293653 PO8064 6312107 PO9389 6227653 PO9391 6234609PP0888 6238040 PP0891 6188415 PP0890 6227654 PP0873 6209989 PP09936247791 PP0890 6336710 PP1398 6217153 PP2592 6416167 PP2593 6243113PP3991 6283581 PP3987 6247790 PP3985 6260953 PP3983 6267469 PO79356224780 PO7936 6235212 PO7937 6280643 PO8061 6284147 PO8054 6214244PO8065 6071750 PO8055 6267905 PO8053 6251298 PO8078 6258285 PO79336225138 PO7950 6241904 PO7949 6299786 PO8060 6866789 PO8059 6231773PO8073 6190931 PO8076 6248249 PO8075 6290862 PO8079 6241906 PO80506565762 PO8052 6241905 PO7948 6451216 PO7951 6231772 PO8074 6274056PO7941 6290861 PO8077 6248248 PO8058 6306671 PO8051 6331258 PO80456110754 PO7952 6294101 PO8046 6416679 PO9390 6264849 PO9392 6254793PP0889 6235211 PP0887 6491833 PP0882 6264850 PP0874 6258284 PP13966312615 PP3989 6228668 PP2591 6180427 PP3990 6171875 PP3986 6267904PP3984 6245247 PP3982 6315914 PP0895 6231148 PP0869 6293658 PP08876614560 PP0885 6238033 PP0884 6312070 PP0886 6238111 PP0877 6378970PP0878 6196739 PP0883 6270182 PP0880 6152619 PO8006 6087638 PO80076340222 PO8010 6041600 PO8011 6299300 PO7947 6067797 PO7944 6286935PO7946 6044646 PP0894 6382769Not applicable.

FIELD OF THE INVENTION

The present invention relates to the field of inkjet printers and,discloses an inkjet printing system using printheads manufactured withmicroelectro-mechanical systems (MEMS) techniques.

BACKGROUND OF THE INVENTION

Many different types of printing have been invented, a large number ofwhich are presently in use. The known forms of print have a variety ofmethods for marking the print media with a relevant marking media.Commonly used forms of printing include offset printing, laser printingand copying devices, dot matrix type impact printers, thermal paperprinters, film recorders, thermal wax printers, dye sublimation printersand ink jet printers both of the drop on demand and continuous flowtype. Each type of printer has its own advantages and problems whenconsidering cost, speed, quality, reliability, simplicity ofconstruction and operation etc.

In recent years, the field of ink jet printing, wherein each individualpixel of ink is derived from one or more ink nozzles has becomeincreasingly popular primarily due to its inexpensive and versatilenature.

Many different techniques on inkjet printing have been invented. For asurvey of the field, reference is made to an article by J Moore,“Non-Impact Printing: Introduction and Historical Perspective”, OutputHard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).

Ink Jet printers themselves come in many different types. Theutilization of a continuous stream of ink in ink jet printing appears todate back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hanselldiscloses a simple form of continuous stream electro-static ink jetprinting.

U.S. Pat. No. 3,596,275 by Sweet also discloses a process of acontinuous inkjet printing including the step wherein the inkjet streamis modulated by a high frequency electrostatic field so as to cause dropseparation. This technique is still utilized by several manufacturersincluding Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweetet al).

Piezoelectric inkjet printers are also one form of commonly utilizedinkjet printing device. Piezoelectric systems are disclosed by Kyser et.al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode ofoperation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses asqueeze mode of operation of a piezoelectric crystal, Stemme in U.S.Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectricoperation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectricpush mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No.4,584,590 which discloses a shear mode type of piezoelectric transducerelement.

Recently, thermal inkjet printing has become an extremely popular formof inkjet printing. The inkjet printing techniques include thosedisclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S.Pat. No. 4,490,728. Both the aforementioned references disclosed ink jetprinting techniques that rely upon the activation of an electrothermalactuator which results in the creation of a bubble in a constrictedspace, such as a nozzle, which thereby causes the ejection of ink froman aperture connected to the confined space onto a relevant print media.Printing devices utilizing the electro-thermal actuator are manufacturedby manufacturers such as Canon and Hewlett Packard.

As can be seen from the foregoing, many different types of printingtechnologies are available. Ideally, a printing technology should have anumber of desirable attributes. These include inexpensive constructionand operation, high speed operation, safe and continuous long termoperation etc. Each technology may have its own advantages anddisadvantages in the areas of cost, speed, quality, reliability, powerusage, simplicity of construction operation, durability and consumables.

In the construction of any inkjet printing system, there are aconsiderable number of important factors which must be traded offagainst one another especially as large scale printheads areconstructed, especially those of a pagewidth type. A number of thesefactors are outlined in the following paragraphs.

Firstly, inkjet printheads are normally constructed utilizingmicro-electromechanical systems (MEMS) techniques. As such, they tend torely upon standard integrated circuit construction/fabricationtechniques of depositing planar layers on a silicon wafer and etchingcertain portions of the planar layers. Within silicon circuitfabrication technology, certain techniques are better known than others.For example, the techniques associated with the creation of CMOScircuits are likely to be more readily used than those associated withthe creation of exotic circuits including ferroelectrics, galiumarsenide etc. Hence, it is desirable, in any MEMS constructions, toutilize well proven semi-conductor fabrication techniques which do notrequire any “exotic” processes or materials. Of course, a certain degreeof trade off will be undertaken in that if the advantages of using theexotic material far out weighs its disadvantages then it may becomedesirable to utilize the material anyway. However, if it is possible toachieve the same, or similar, properties using more common materials,the problems of exotic materials can be avoided.

With a large array of ink ejection nozzles, it is desirable to providefor a highly automated form of manufacturing which results in aninexpensive production of multiple printhead devices.

Preferably, the device constructed utilizes a low amount of energy inthe ejection of ink. The utilization of a low amount of energy isparticularly important when a large pagewidth full color printhead isconstructed having a large array of individual print ejection mechanismwith each ejection mechanisms, in the worst case, being fired in a rapidsequence.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an ink ejectionnozzle arrangement suitable for incorporation into an inkjet printheadarrangement for the ejection of ink on demand from a nozzle chamber inan efficient and reliable manner.

According to a first aspect, the present invention provides an ink jetprinthead comprising:

a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzlesrespectively, the bubble forming chambers adapted to contain a bubbleforming liquid; and,

at least one heater element disposed in each of the bubble formingchambers respectively, the heater elements configured for thermalcontact with the bubble forming liquid; such that,

heating the heater element to a temperature above the boiling point ofthe bubble forming liquid forms a gas bubble that causes the ejection ofa drop of an ejectable liquid through the nozzle corresponding to thatheater element; wherein,

the bubble forming chamber is at least partially formed by an amorphousceramic material.

Amorphous ceramic material provides the bubble forming chamber with highstrength. The non-crystalline structure avoids any points of weaknessdue to crystalline defects. These defects can act as stressconcentration areas and are prone to failure.

According to a second aspect, the present invention provides a printersystem which incorporates a printhead, the printhead comprising:

a plurality of nozzles;

a bubble forming chamber corresponding to each of the nozzlesrespectively, the bubble forming chambers adapted to contain a bubbleforming liquid; and,

at least one heater element disposed in each of the bubble formingchambers respectively, the heater elements configured for thermalcontact with the bubble forming liquid; such that,

heating the heater element to a temperature above the boiling point ofthe bubble forming liquid forms a gas bubble that causes the ejection ofa drop of an ejectable liquid through the nozzle corresponding to thatheater element; wherein,

the bubble forming chamber is at least partially formed by an amorphousceramic material.

According to a third aspect, the present invention provides a method ofejecting drops of an ejectable liquid from a printhead, the printheadcomprising a plurality of nozzles;

-   a chamber corresponding to each of the nozzles respectively, the    chambers adapted to contain an ejectable liquid; and,-   at least one droplet ejection actuator associated with each of the    chambers respectively; wherein,-   the chamber is at least partially formed by an amorphous ceramic    material;-   the method comprising the steps of:

placing the ejectable liquid into contact with the drop ejectionactuator; and

-   actuating the droplet ejection actuator such that a droplet of an    ejectable liquid is ejected through the corresponding nozzle.

Preferably, the amorphous ceramic material is silicon nitride. Inanother form, the amorphous ceramic material is silicon dioxide. In yetanother embodiment, the amorphous ceramic material is siliconoxynitride.

Preferably, the thermal actuator units are interconnected at a first endto a substrate and at a second end to a rigid strut member. The rigidstrut member can, in turn, be interconnected to the arm having one endattached to the paddle vane. The thermal actuator units can operate uponconductive heating along a conductive trace and the conductive heatingcan include the generation of a substantial portion of the heat in thearea adjacent the first end. The conductive heating trace can include athinned cross-section adjacent the first end. The heating layers of thethermal actuator units can comprise substantially either a copper nickelalloy or titanium nitride. The paddle can be constructed from a similarconductive material to portions of the thermal actuator units however itis conductively insulated therefrom.

Preferably, the thermal actuator units are constructed from multiplelayers utilizing a single mask to etch the multiple layers.

The nozzle chamber can include an actuator access port in a secondsurface of the chamber. The access port can comprise a slot in a cornerof the chamber and the actuator is able to move in an arc through theslot. The actuator can include an end portion that mates substantiallywith a wall of the chamber at substantially right angles to the paddlevane. The paddle vane can include a depressed portion substantiallyopposite the fluid ejection port.

In accordance with a further aspect of the present invention, there isprovided a thermal actuator including a series of lever arms attached atone end to a substrate, the thermal actuator being operational as aresult of conductive heating of a conductive trace, the conductive traceincluding a thinned cross-section substantially adjacent the attachmentto the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Notwithstanding any other forms that may fall within the scope of thepresent invention, preferred forms of the invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings in which:

FIG. 1 is a schematic cross-sectional view through an ink chamber of aunit cell of a printhead according to an embodiment using a bubbleforming heater element;

FIG. 2 is a schematic cross-sectional view through the ink chamber FIG.1, at another stage of operation;

FIG. 3 is a schematic cross-sectional view through the ink chamber FIG.1, at yet another stage of operation;

FIG. 4 is a schematic cross-sectional view through the ink chamber FIG.1, at yet a further stage of operation; and

FIG. 5 is a diagrammatic cross-sectional view through a unit cell of aprinthead in accordance with an embodiment of the invention showing thecollapse of a vapor bubble.

FIG. 6 is a schematic, partially cut away, perspective view of a furtherembodiment of a unit cell of a printhead.

FIG. 7 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 6.

FIG. 8 is a schematic, partially cut away, perspective view of a furtherembodiment of a unit cell of a printhead.

FIG. 9 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 8.

FIG. 10 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 11 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 10.

FIG. 12 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 13 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 14 is a schematic, partially cut away, exploded perspective view ofthe unit cell of FIG. 13.

FIGS. 15 to 25 are schematic perspective views of the unit cell shown inFIGS. 13 and 14, at various successive stages in the production processof the printhead.

FIGS. 26 and 27 show schematic, partially cut away, schematicperspective views of two variations of the unit cell of FIGS. 13 to 25.

FIG. 28 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

FIG. 29 is a schematic, partially cut away, perspective view of afurther embodiment of a unit cell of a printhead.

DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

Bubble Forming Heater Element Actuator

With reference to FIGS. 1 to 4, the unit cell 1 of a printhead accordingto an embodiment of the invention comprises a nozzle plate 2 withnozzles 3 therein, the nozzles having nozzle rims 4, and apertures 5extending through the nozzle plate. The nozzle plate 2 is plasma etchedfrom a silicon nitride structure which is deposited, by way of chemicalvapor deposition (CVD), over a sacrificial material which issubsequently etched.

The printhead also includes, with respect to each nozzle 3, side walls 6on which the nozzle plate is supported, a chamber 7 defined by the wallsand the nozzle plate 2, a multi-layer substrate 8 and an inlet passage 9extending through the multi-layer substrate to the far side (not shown)of the substrate. A looped, elongate heater element 10 is suspendedwithin the chamber 7, so that the element is in the form of a suspendedbeam. The printhead as shown is a microelectromechanical system (MEMS)structure, which is formed by a lithographic process which is describedin more detail below.

When the printhead is in use, ink 11 from a reservoir (not shown) entersthe chamber 7 via the inlet passage 9, so that the chamber fills to thelevel as shown in FIG. 1. Thereafter, the heater element 10 is heatedfor somewhat less than 1 microsecond, so that the heating is in the formof a thermal pulse. It will be appreciated that the heater element 10 isin thermal contact with the ink 11 in the chamber 7 so that when theelement is heated, this causes the generation of vapor bubbles 12 in theink. Accordingly, the ink 11 constitutes a bubble forming liquid. FIG. 1shows the formation of a bubble 12 approximately 1 microsecond aftergeneration of the thermal pulse, that is, when the bubble has justnucleated on the heater elements 10. It will be appreciated that, as theheat is applied in the form of a pulse, all the energy necessary togenerate the bubble 12 is to be supplied within that short time.

When the element 10 is heated as described above, the bubble 12 formsalong the length of the element, this bubble appearing, in thecross-sectional view of FIG. 1, as four bubble portions, one for each ofthe element portions shown in cross section.

The bubble 12, once generated, causes an increase in pressure within thechamber 7, which in turn causes the ejection of a drop 16 of the ink 11through the nozzle 3. The rim 4 assists in directing the drop 16 as itis ejected, so as to minimize the chance of drop misdirection.

The reason that there is only one nozzle 3 and chamber 7 per inletpassage 9 is so that the pressure wave generated within the chamber, onheating of the element 10 and forming of a bubble 12, does not affectadjacent chambers and their corresponding nozzles. The pressure wavegenerated within the chamber creates significant stresses in the chamberwall. Forming the chamber from an amorphous ceramic such as siliconnitride, silicon dioxide (glass) or silicon oxynitride, gives thechamber walls high strength while avoiding the use of material with acrystal structure. Crystalline defects can act as stress concentrationpoints and therefore potential areas of weakness and ultimately failure.

FIGS. 2 and 3 show the unit cell 1 at two successive later stages ofoperation of the printhead. It can be seen that the bubble 12 generatesfurther, and hence grows, with the resultant advancement of ink 11through the nozzle 3. The shape of the bubble 12 as it grows, as shownin FIG. 3, is determined by a combination of the inertial dynamics andthe surface tension of the ink 11. The surface tension tends to minimizethe surface area of the bubble 12 so that, by the time a certain amountof liquid has evaporated, the bubble is essentially disk-shaped.

The increase in pressure within the chamber 7 not only pushes ink 11 outthrough the nozzle 3, but also pushes some ink back through the inletpassage 9. However, the inlet passage 9 is approximately 200 to 300microns in length, and is only approximately 16 microns in diameter.Hence there is a substantial viscous drag. As a result, the predominanteffect of the pressure rise in the chamber 7 is to force ink out throughthe nozzle 3 as an ejected drop 16, rather than back through the inletpassage 9.

Turning now to FIG. 4, the printhead is shown at a still furthersuccessive stage of operation, in which the ink drop 16 that is beingejected is shown during its “necking phase” before the drop breaks off.At this stage, the bubble 12 has already reached its maximum size andhas then begun to collapse towards the point of collapse 17, asreflected in more detail in FIG. 21.

The collapsing of the bubble 12 towards the point of collapse 17 causessome ink 11 to be drawn from within the nozzle 3 (from the sides 18 ofthe drop), and some to be drawn from the inlet passage 9, towards thepoint of collapse. Most of the ink 11 drawn in this manner is drawn fromthe nozzle 3, forming an annular neck 19 at the base of the drop 16prior to its breaking off.

The drop 16 requires a certain amount of momentum to overcome surfacetension forces, in order to break off. As ink 11 is drawn from thenozzle 3 by the collapse of the bubble 12, the diameter of the neck 19reduces thereby reducing the amount of total surface tension holding thedrop, so that the momentum of the drop as it is ejected out of thenozzle is sufficient to allow the drop to break off.

When the drop 16 breaks off, cavitation forces are caused as reflectedby the arrows 20, as the bubble 12 collapses to the point of collapse17. It will be noted that there are no solid surfaces in the vicinity ofthe point of collapse 17 on which the cavitation can have an effect.

Features and Advantages of Further Embodiments

FIGS. 6 to 29 show further embodiments of unit cells 1 for thermalinkjet printheads, each embodiment having its own particular functionaladvantages. These advantages will be discussed in detail below, withreference to each individual embodiment. For consistency, the samereference numerals are used in FIGS. 6 to 29 to indicate correspondingcomponents.

Referring to FIGS. 6 and 7, the unit cell 1 shown has the chamber 7, inksupply passage 32 and the nozzle rim 4 positioned mid way along thelength of the unit cell 1. As best seen in FIG. 7, the drive circuitry22 is partially on one side of the chamber 7 with the remainder on theopposing side of the chamber. The drive circuitry 22 controls theoperation of the heater 14 through vias in the integrated circuitmetallisation layers of the interconnect 23. The interconnect 23 has araised metal layer on its top surface. Passivation layer 24 is formed intop of the interconnect 23 but leaves areas of the raised metal layerexposed. Electrodes 15 of the heater 14 contact the exposed metal areasto supply power to the element 10.

Alternatively, the drive circuitry 22 for one unit cell is not onopposing sides of the heater element that it controls. All the drivecircuitry 22 for the heater 14 of one unit cell is in a single,undivided area that is offset from the heater. That is, the drivecircuitry 22 is partially overlaid by one of the electrodes 15 of theheater 14 that it is controlling, and partially overlaid by one or moreof the heater electrodes 15 from adjacent unit cells. In this situation,the center of the drive circuitry 22 is less than 200 microns from thecenter of the associate nozzle aperture 5. In most Memjet printheads ofthis type, the offset is less than 100 microns and in many cases lessthan 50 microns, preferably less than 30 microns.

Configuring the nozzle components so that there is significant overlapbetween the electrodes and the drive circuitry provides a compact designwith high nozzle density (nozzles per unit area of the nozzle plate 2).This also improves the efficiency of the printhead by shortening thelength of the conductors from the circuitry to the electrodes. Theshorter conductors have less resistance and therefore dissipate lessenergy.

The high degree of overlap between the electrodes 15 and the drivecircuitry 22 also allows more vias between the heater material and theCMOS metalization layers of the interconnect 23. As best shown in FIGS.14 and 15, the passivation layer 24 has an array of vias to establish anelectrical connection with the heater 14. More vias lowers theresistance between the heater electrodes 15 and the interconnect layer23 which reduces power losses. However, the passivation layer 24 andelectrodes 15 may also be provided without vias in order to simplify thefabrication process.

In FIGS. 8 and 9, the unit cell 1 is the same as that of FIGS. 6 and 7apart from the heater element 10. The heater element 10 has a bubblenucleation section 158 with a smaller cross section than the remainderof the element. The bubble nucleation section 158 has a greaterresistance and heats to a temperature above the boiling point of the inkbefore the remainder of the element 10. The gas bubble nucleates at thisregion and subsequently grows to surround the rest of the element 10. Bycontrolling the bubble nucleation and growth, the trajectory of theejected drop is more predictable.

The heater element 10 is configured to accommodate thermal expansion ina specific manner. As heater elements expand, they will deform torelieve the strain. Elements such as that shown in FIGS. 6 and 7 willbow out of the plane of lamination because its thickness is the thinnestcross sectional dimension and therefore has the least bendingresistance. Repeated bending of the element can lead to the formation ofcracks, especially at sharp corners, which can ultimately lead tofailure. The heater element 10 shown in FIGS. 8 and 9 is configured sothat the thermal expansion is relieved by rotation of the bubblenucleation section 158, and slightly splaying the sections leading tothe electrodes 15, in preference to bowing out of the plane oflamination. The geometry of the element is such that miniscule bendingwithin the plane of lamination is sufficient to relieve the strain ofthermal expansion, and such bending occurs in preference to bowing. Thisgives the heater element greater longevity and reliability by minimizingbend regions, which are prone to oxidation and cracking.

Referring to FIGS. 10 and 11, the heater element 10 used in this unitcell 1 has a serpentine or ‘double omega’ shape. This configurationkeeps the gas bubble centered on the axis of the nozzle. A single omegais a simple geometric shape which is beneficial from a fabricationperspective. However the gap 159 between the ends of the heater elementmeans that the heating of the ink in the chamber is slightlyasymmetrical. As a result, the gas bubble is slightly skewed to the sideopposite the gap 159. This can in turn affect the trajectory of theejected drop. The double omega shape provides the heater element withthe gap 160 to compensate for the gap 159 so that the symmetry andposition of the bubble within the chamber is better controlled and theejected drop trajectory is more reliable.

FIG. 12 shows a heater element 10 with a single omega shape. Asdiscussed above, the simplicity of this shape has significant advantagesduring lithographic fabrication. It can be a single current path that isrelatively wide and therefore less affected by any inherent inaccuraciesin the deposition of the heater material. The inherent inaccuracies ofthe equipment used to deposit the heater material result in variationsin the dimensions of the element. However, these tolerances are fixedvalues so the resulting variations in the dimensions of a relativelywide component are proportionally less than the variations for a thinnercomponent. It will be appreciated that proportionally large changes ofcomponents dimensions will have a greater effect on their intendedfunction. Therefore the performance characteristics of a relatively wideheater element are more reliable than a thinner one.

The omega shape directs current flow around the axis of the nozzleaperture 5. This gives good bubble alignment with the aperture forbetter ejection of drops while ensuring that the bubble collapse pointis not on the heater element 10. As discussed above, this avoidsproblems caused by cavitation.

Referring to FIGS. 13 to 26, another embodiment of the unit cell 1 isshown together with several stages of the etching and depositionfabrication process. In this embodiment, the heater element 10 issuspended from opposing sides of the chamber. This allows it to besymmetrical about two planes that intersect along the axis of the nozzleaperture 5. This configuration provides a drop trajectory along the axisof the nozzle aperture 5 while avoiding the cavitation problemsdiscussed above. FIGS. 27 and 28 show other variations of this type ofheater element 10.

FIG. 28 shows a unit cell 1 that has the nozzle aperture 5 and theheater element 10 offset from the center of the nozzle chamber 7.Consequently, the nozzle chamber 7 is larger than the previousembodiments. The heater 14 has two different electrodes 15 with theright hand electrode 15 extending well into the nozzle chamber 7 tosupport one side of the heater element 10. This reduces the area of thevias contacting the electrodes which can increase the electroderesistance and therefore the power losses. However, laterally offsettingthe heater element from the ink inlet 31 increases the fluidic dragretarding flow back through the inlet 31 and ink supply passage 32. Thefluidic drag through the nozzle aperture 5 comparatively much smaller solittle energy is lost to a reverse flow of ink through the inlet when agas bubble form on the element 10.

The unit cell 1 shown in FIG. 29 also has a relatively large chamber 7which again reduces the surface area of the electrodes in contact withthe vias leading to the interconnect layer 23. However, the largerchamber 7 allows several heater elements 10 offset from the nozzleaperture 5. The arrangement shown uses two heater elements 10; one oneither side of the chamber 7. Other designs use three or more elementsin the chamber. Gas bubbles nucleate from opposing sides of the nozzleaperture and converge to form a single bubble. The bubble formed issymmetrical about at least one plane extending along the nozzle axis.This enhances the control of the symmetry and position of the bubblewithin the chamber 7 and therefore the ejected drop trajectory is morereliable.

Fabrication Process

In the interests of brevity, the fabrication stages have been shown forthe unit cell of FIG. 13 only (see FIGS. 15 to 25). It will beappreciated that the other unit cells will use the same fabricationstages with different masking.

Referring to FIG. 15, there is shown the starting point for fabricationof the thermal inkjet nozzle shown in FIG. 13. CMOS processing of asilicon wafer provides a silicon substrate 21 having drive circuitry 22,and an interlayer dielectric (“interconnect”) 23. The interconnect 23comprises four metal layers, which together form a seal ring for theinlet passage 9 to be etched through the interconnect. The top metallayer 26, which forms an upper portion of the seal ring, can be seen inFIG. 15. The metal seal ring prevents ink moisture from seeping into theinterconnect 23 when the inlet passage 9 is filled with ink.

A passivation layer 24 is deposited onto the top metal layer 26 byplasma-enhanced chemical vapour deposition (PECVD). After deposition ofthe passivation layer 24, it is etched to define a circular recess,which forms parts of the inlet passage 9. At the same as etching therecess, a plurality of vias 50 are also etched, which allow electricalconnection through the passivation layer 24 to the top metal layer 26.The etch pattern is defined by a layer of patterned photoresist (notshown), which is removed by O₂ ashing after the etch.

Referring to FIG. 16, in the next fabrication sequence, a layer ofphotoresist is spun onto the passivation later 24. The photoresist isexposed and developed to define a circular opening. With the patternedphotoresist 51 in place, the dielectric interconnect 23 is etched as faras the silicon substrate 21 using a suitable oxide-etching gas chemistry(e.g. O₂/C₄F₈). Etching through the silicon substrate is continued downto about 20 microns to define a front ink hole 52, using a suitablesilicon-etching gas chemistry (e.g. ‘Bosch etch’). The same photoresistmask 51 can be used for both etching steps. FIG. 17 shows the unit cellafter etching the front ink hole 52 and removal of the photoresist 51.

Referring to FIG. 18, in the next stage of fabrication, the front inkhole 52 is plugged with photoresist to provide a front plug 53. At thesame time, a layer of photoresist is deposited over the passivationlayer 24. This layer of photoresist is exposed and developed to define afirst sacrificial scaffold 54 over the front plug 53, and scaffoldingtracks 35 around the perimeter of the unit cell. The first sacrificialscaffold 54 is used for subsequent deposition of heater material 38thereon and is therefore formed with a planar upper surface to avoid anybuckling in the heater element (see heater element 10 in FIG. 13). Thefirst sacrificial scaffold 54 is UV cured and hardbaked to preventreflow of the photoresist during subsequent high-temperature depositiononto its upper surface.

Importantly, the first sacrificial scaffold 54 has sloped or angled sidefaces 55. These angled side faces 55 are formed by adjusting thefocusing in the exposure tool (e.g. stepper) when exposing thephotoresist. The sloped side faces 55 advantageously allow heatermaterial 38 to be deposited substantially evenly over the firstsacrificial scaffold 54.

Referring to FIG. 19, the next stage of fabrication deposits the heatermaterial 38 over the first sacrificial scaffold 54, the passivationlayer 24 and the perimeter scaffolding tracks 35. The heater material 38is typically a monolayer of TiAlN. However, the heater material 38 mayalternatively comprise TiAlN sandwiched between upper and lowerpassivating materials, such as tantalum or tantalum nitride. Passivatinglayers on the heater element 10 minimize corrosion of the and improveheater longevity.

Referring to FIG. 20, the heater material 38 is subsequently etched downto the first sacrificial scaffold 54 to define the heater element 10. Atthe same time, contact electrodes 15 are defined on either side of theheater element 10. The electrodes 15 are in contact with the top metallayer 26 and so provide electrical connection between the CMOS and theheater element 10. The sloped side faces of the first sacrificialscaffold 54 ensure good electrical connection between the heater element10 and the electrodes 15, since the heater material is deposited withsufficient thickness around the scaffold 54. Any thin areas of heatermaterial (due to insufficient side face deposition) would increaseresistivity and affect heater performance.

Adjacent unit cells are electrically insulated from each other by virtueof grooves etched around the perimeter of each unit cell. The groovesare etched at the same time as defining the heater element 10.

Referring to FIG. 21, in the subsequent step a second sacrificialscaffold 39 of photoresist is deposited over the heater material. Thesecond sacrificial scaffold 39 is exposed and developed to definesidewalls for the cylindrical nozzle chamber and perimeter sidewalls foreach unit cell. The second sacrificial scaffold 39 is also UV cured andhardbaked to prevent any reflow of the photoresist during subsequenthigh-temperature deposition of the silicon nitride roof material.

Referring to FIG. 22, silicon nitride is deposited onto the secondsacrificial scaffold 39 by plasma enhanced chemical vapour deposition.The silicon nitride forms a roof 44 over each unit cell, which is thenozzle plate 2 for a row of nozzles. Chamber sidewalls 6 and unit cellsidewalls 56 are also formed by deposition of silicon nitride.

Referring to FIG. 23, the nozzle rim 4 is etched partially through theroof 44, by placing a suitably patterned photoresist mask over the roof,etching for a controlled period of time and removing the photoresist byashing.

Referring to FIG. 24, the nozzle aperture 5 is etched through the roof24 down to the second sacrificial scaffold 39. Again, the etch isperformed by placing a suitably patterned photoresist mask over theroof, etching down to the scaffold 39 and removing the photoresist mask.

With the nozzle structure now fully formed on a frontside of the siliconsubstrate 21, an ink supply channel 32 is etched from the backside ofthe substrate 21, which meets with the front plug 53.

Referring to FIG. 25, after formation of the ink supply channel 32, thefirst and second sacrificial scaffolds of photoresist, together with thefront plug 53 are ashed off using an O₂ plasma. Accordingly, fluidconnection is made from the ink supply channel 32 through to the nozzleaperture 5.

It should be noted that a portion of photoresist, on either side of thenozzle chamber sidewalls 6, remains encapsulated by the roof 44, theunit cell sidewalls 56 and the chamber sidewalls 6. This portion ofphotoresist is sealed from the O₂ ashing plasma and, therefore, remainsintact after fabrication of the printhead. This encapsulated photoresistadvantageously provides additional robustness for the printhead bysupporting the nozzle plate 2. Hence, the printhead has a robust nozzleplate spanning continuously over rows of nozzles, and being supported bysolid blocks of hardened photoresist, in addition to support walls.

Other Embodiments

The invention has been described above with reference to printheadsusing bubble forming heater elements. However, it is potentially suitedto a wide range of printing system including: color and monochromeoffice printers, short run digital printers, high speed digitalprinters, offset press supplemental printers, low cost scanning printershigh speed pagewidth printers, notebook computers with inbuilt pagewidthprinters, portable color and monochrome printers, color and monochromecopiers, color and monochrome facsimile machines, combined printer,facsimile and copying machines, label printers, large format plotters,photograph copiers, printers for digital photographic “minilabs”, videoprinters, PHOTO CD (PHOTO CD is a registered trade mark of the EastmanKodak Company) printers, portable printers for PDAs, wallpaper printers,indoor sign printers, billboard printers, fabric printers, cameraprinters and fault tolerant commercial printer arrays.

It will be appreciated by ordinary workers in this field that numerousvariations and/or modifications may be made to the present invention asshown in the specific embodiments without departing from the spirit orscope of the invention as broadly described. The present embodimentsare, therefore, to be considered in all respects to be illustrative andnot restrictive.

Ink Jet Technologies

The embodiments of the invention use an ink jet printer type device. Ofcourse many different devices could be used. However presently popularink jet printing technologies are unlikely to be suitable.

The most significant problem with thermal ink jet is power consumption.This is approximately 100 times that required for high speed, and stemsfrom the energy-inefficient means of drop ejection. This involves therapid boiling of water to produce a vapor bubble which expels the ink.Water has a very high heat capacity, and must be superheated in thermalink jet applications. In conventional thermal inkjet printheads, thisleads to an efficiency of around 0.02%, from electricity input to dropmomentum (and increased surface area) out.

The most significant problem with piezoelectric ink jet is size andcost. Piezoelectric crystals have a very small deflection at reasonabledrive voltages, and therefore require a large area for each nozzle.Also, each piezoelectric actuator must be connected to its drive circuiton a separate substrate. This is not a significant problem at thecurrent limit of around 300 nozzles per printhead, but is a majorimpediment to the fabrication of pagewidth printheads with 19,200nozzles.

Ideally, the ink jet technologies used meet the stringent requirementsof in-camera digital color printing and other high quality, high speed,low cost printing applications. To meet the requirements of digitalphotography, new ink jet technologies have been created. The targetfeatures include:

low power (less than 10 Watts)

high resolution capability (1,600 dpi or more)

photographic quality output

low manufacturing cost

small size (pagewidth times minimum cross section)

high speed (<2 seconds per page).

All of these features can be met or exceeded by the ink jet systemsdescribed below with differing levels of difficulty. Forty-fivedifferent ink jet technologies have been developed by the Assignee togive a wide range of choices for high volume manufacture. Thesetechnologies form part of separate applications assigned to the presentAssignee as set out in the table under the heading Cross References toRelated Applications.

The ink jet designs shown here are suitable for a wide range of digitalprinting systems, from battery powered one-time use digital cameras,through to desktop and network printers, and through to commercialprinting systems.

For ease of manufacture using standard process equipment, the printheadis designed to be a monolithic 0.5 micron CMOS chip with MEMS postprocessing. For color photographic applications, the printhead is 100 mmlong, with a width which depends upon the ink jet type. The smallestprinthead designed is IJ38, which is 0.35 mm wide, giving a chip area of35 square mm. The printheads each contain 19,200 nozzles plus data andcontrol circuitry.

Ink is supplied to the back of the printhead by injection molded plasticink channels. The molding requires 50 micron features, which can becreated using a lithographically micromachined insert in a standardinjection molding tool. Ink flows through holes etched through the waferto the nozzle chambers fabricated on the front surface of the wafer. Theprinthead is connected to the camera circuitry by tape automatedbonding.

Tables of Drop-on-Demand Ink Jets

Eleven important characteristics of the fundamental operation ofindividual ink jet nozzles have been identified. These characteristicsare largely orthogonal, and so can be elucidated as an elevendimensional matrix. Most of the eleven axes of this matrix includeentries developed by the present assignee.

The following tables form the axes of an eleven dimensional table of inkjet types.

Actuator mechanism (18 types)

Basic operation mode (7 types)

Auxiliary mechanism (8 types)

Actuator amplification or modification method (17 types)

Actuator motion (19 types)

Nozzle refill method (4 types)

Method of restricting back-flow through inlet (10 types)

Nozzle clearing method (9 types)

Nozzle plate construction (9 types)

Drop ejection direction (5 types)

Ink type (7 types)

The complete eleven dimensional table represented by these axes contains36.9 billion possible configurations of ink jet nozzle. While not all ofthe possible combinations result in a viable ink jet technology, manymillion configurations are viable. It is clearly impractical toelucidate all of the possible configurations. Instead, certain ink jettypes have been investigated in detail. These are designated IJ01 toIJ45 above which matches the docket numbers in the table under theheading Cross References to Related Applications.

Other ink jet configurations can readily be derived from theseforty-five examples by substituting alternative configurations along oneor more of the 11 axes. Most of the IJ01 to IJ45 examples can be madeinto ink jet printheads with characteristics superior to any currentlyavailable ink jet technology.

Where there are prior art examples known to the inventor, one or more ofthese examples are listed in the examples column of the tables below.The IJ01 to IJ45 series are also listed in the examples column. In somecases, print technology may be listed more than once in a table, whereit shares characteristics with more than one entry.

Suitable applications for the ink jet technologies include: Homeprinters, Office network printers, Short run digital printers,Commercial print systems, Fabric printers, Pocket printers, Internet WWWprinters, Video printers, Medical imaging, Wide format printers,Notebook PC printers, Fax machines, Industrial printing systems,Photocopiers, Photographic minilabs etc.

The information associated with the aforementioned 11 dimensional matrixare set out in the following tables.

ACTUATOR MECHANISM (APPLIED ONLY TO SELECTED INK DROPS) DescriptionAdvantages Disadvantages Examples Thermal An electrothermal Large forceHigh power Canon Bubblejet bubble heater heats the ink to generated Inkcarrier 1979 Endo et al GB above boiling point, Simple limited to waterpatent 2,007,162 transferring significant construction Low efficiencyXerox heater-in- heat to the aqueous No moving parts High pit 1990Hawkins et ink. A bubble Fast operation temperatures al U.S. Pat. No.nucleates and quickly Small chip area required 4,899,181 forms,expelling the required for actuator High mechanical Hewlett-Packard ink.stress TIJ 1982 Vaught et The efficiency of the Unusual al U.S. Pat. No.process is low, with materials required 4,490,728 typically less thanLarge drive 0.05% of the electrical transistors energy being Cavitationcauses transformed into actuator failure kinetic energy of the Kogationreduces drop. bubble formation Large print heads are difficult tofabricate Piezo- A piezoelectric crystal Low power Very large area Kyseret al electric such as lead consumption required for actuator U.S. Pat.No. 3,946,398 lanthanum zirconate Many ink types Difficult to ZoltanU.S. Pat. (PZT) is electrically can be used integrate with No. 3,683,212activated, and either Fast operation electronics 1973 Stemme expands,shears, or High efficiency High voltage U.S. Pat. No. 3,747,120 bends toapply drive transistors Epson Stylus pressure to the ink, requiredTektronix ejecting drops. Full pagewidth IJ04 print heads impracticaldue to actuator size Requires electrical poling in high field strengthsduring manufacture Electro- An electric field is Low power Low maximumSeiko Epson, strictive used to activate consumption strain (approx. Usuiet all JP electrostriction in Many ink types 0.01%) 253401/96 relaxormaterials such can be used Large area IJ04 as lead lanthanum Low thermalrequired for actuator zirconate titanate expansion due to low strain(PLZT) or lead Electric field Response speed magnesium niobate strengthrequired is marginal (PMN). (approx. 3.5 V/μm) (~10 μs) can be generatedHigh voltage without difficulty drive transistors Does not requirerequired electrical poling Full pagewidth print heads impractical due toactuator size Ferro- An electric field is Low power Difficult to IJ04electric used to induce a phase consumption integrate with transitionbetween the Many ink types electronics antiferroelectric (AFE) can beused Unusual and ferroelectric (FE) Fast operation materials such asphase. Perovskite (<1 μs) PLZSnT are materials such as tin Relativelyhigh required modified lead longitudinal strain Actuators requirelanthanum zirconate High efficiency a large area titanate (PLZSnT)Electric field exhibit large strains of strength of around 3 up to 1%associated V/μm can be with the AFE to FE readily provided phasetransition. Electro- Conductive plates are Low power Difficult to IJ02,IJ04 static plates separated by a consumption operate electrostaticcompressible or fluid Many ink types devices in an dielectric (usuallyair). can be used aqueous Upon application of a Fast operationenvironment voltage, the plates The electrostatic attract each other andactuator will displace ink, causing normally need to be drop ejection.The separated from the conductive plates may ink be in a comb or Verylarge area honeycomb structure, required to achieve or stacked toincrease high forces the surface area and High voltage therefore theforce. drive transistors may be required Full pagewidth print heads arenot competitive due to actuator size Electro- A strong electric fieldLow current High voltage 1989 Saito et al, static pull is applied to theink, consumption required U.S. Pat. No. 4,799,068 on ink whereupon Lowtemperature May be damaged 1989 Miura et al, electrostatic attraction bysparks due to air U.S. Pat. No. 4,810,954 accelerates the ink breakdownTone-jet towards the print Required field medium. strength increases asthe drop size decreases High voltage drive transistors requiredElectrostatic field attracts dust Permanent An electromagnet Low powerComplex IJ07, IJ10 magnet directly attracts a consumption fabricationelectro- permanent magnet, Many ink types Permanent magnetic displacingink and can be used magnetic material causing drop ejection. Fastoperation such as Neodymium Rare earth magnets High efficiency IronBoron (NdFeB) with a field strength Easy extension required. around 1Tesla can be from single nozzles High local used. Examples are: topagewidth print currents required Samarium Cobalt heads Copper (SaCo)and magnetic metalization should materials in the be used for longneodymium iron boron electromigration family (NdFeB, lifetime and lowNdDyFeBNb, resistivity NdDyFeB, etc) Pigmented inks are usuallyinfeasible Operating temperature limited to the Curie temperature(around 540 K) Soft A solenoid induced a Low power Complex IJ01, IJ05,IJ08, magnetic magnetic field in a soft consumption fabrication IJ10,IJ12, IJ14, core electro- magnetic core or yoke Many ink types Materialsnot IJ15, IJ17 magnetic fabricated from a can be used usually present ina ferrous material such Fast operation CMOS fab such as as electroplatediron High efficiency NiFe, CoNiFe, or alloys such as CoNiFe Easyextension CoFe are required [1], CoFe, or NiFe from single nozzles Highlocal alloys. Typically, the to pagewidth print currents required softmagnetic material heads Copper is in two parts, which metalizationshould are normally held be used for long apart by a spring.electromigration When the solenoid is lifetime and low actuated, the twoparts resistivity attract, displacing the Electroplating is ink.required High saturation flux density is required (2.0-2.1 T isachievable with CoNiFe [1]) Lorenz The Lorenz force Low power Force actsas a IJ06, IJ11, IJ13, force acting on a current consumption twistingmotion IJ16 carrying wire in a Many ink types Typically, only a magneticfield is can be used quarter of the utilized. Fast operation solenoidlength This allows the High efficiency provides force in a magneticfield to be Easy extension useful direction supplied externally to fromsingle nozzles High local the print head, for to pagewidth printcurrents required example with rare heads Copper earth permanentmetalization should magnets. be used for long Only the currentelectromigration carrying wire need be lifetime and low fabricated onthe print- resistivity head, simplifying Pigmented inks materials areusually requirements. infeasible Magneto- The actuator uses the Many inktypes Force acts as a Fischenbeck, striction giant magnetostrictive canbe used twisting motion U.S. Pat. No. 4,032,929 effect of materials Fastoperation Unusual IJ25 such as Terfenol-D Easy extension materials suchas (an alloy of terbium, from single nozzles Terfenol-D are dysprosiumand iron to pagewidth print required developed at the Naval heads Highlocal Ordnance Laboratory, High force is currents required henceTer-Fe-NOL). available Copper For best efficiency, the metalizationshould actuator should be pre- be used for long stressed to approx. 8electromigration MPa. lifetime and low resistivity Pre-stressing may berequired Surface Ink under positive Low power Requires Silverbrook, EPtension pressure is held in a consumption supplementary force 0771 658A2 and reduction nozzle by surface Simple to effect drop related patenttension. The surface construction separation applications tension of theink is No unusual Requires special reduced below the materials requiredin ink surfactants bubble threshold, fabrication Speed may be causingthe ink to High efficiency limited by surfactant egress from the Easyextension properties nozzle. from single nozzles to pagewidth printheads Viscosity The ink viscosity is Simple Requires Silverbrook, EPreduction locally reduced to construction supplementary force 0771 658A2 and select which drops are No unusual to effect drop related patentto be ejected. A materials required in separation applications viscosityreduction can fabrication Requires special be achieved Easy extensionink viscosity electrothermally with from single nozzles properties mostinks, but special to pagewidth print High speed is inks can beengineered heads difficult to achieve for a 100:1 viscosity Requiresreduction. oscillating ink pressure A high temperature difference(typically 80 degrees) is required Acoustic An acoustic wave is Canoperate Complex drive 1993 Hadimioglu generated and without a nozzlecircuitry et al, EUP 550,192 focussed upon the plate Complex 1993 Elrodet al, drop ejection region. fabrication EUP 572,220 Low efficiency Poorcontrol of drop position Poor control of drop volume Thermo- An actuatorwhich Low power Efficient aqueous IJ03, IJ09, IJ17, elastic bend reliesupon differential consumption operation requires a IJ18, IJ19, IJ20,actuator thermal expansion Many ink types thermal insulator on IJ21,IJ22, IJ23, upon Joule heating is can be used the hot side IJ24, IJ27,IJ28, used. Simple planar Corrosion IJ29, IJ30, IJ31, fabricationprevention can be IJ32, IJ33, IJ34, Small chip area difficult IJ35,IJ36, IJ37, required for each Pigmented inks IJ38 ,IJ39, IJ40, actuatormay be infeasible, IJ41 Fast operation as pigment particles Highefficiency may jam the bend CMOS actuator compatible voltages andcurrents Standard MEMS processes can be used Easy extension from singlenozzles to pagewidth print heads High CTE A material with a very Highforce can Requires special IJ09, IJ17, IJ18, thermo- high coefficient ofbe generated material (e.g. PTFE) IJ20, IJ21, IJ22, elastic thermalexpansion Three methods of Requires a PTFE IJ23, IJ24, IJ27, actuator(CTE) such as PTFE deposition are deposition process, IJ28, IJ29, IJ30,polytetrafluoroethylene under development: which is not yet IJ31, IJ42,IJ43, (PTFE) is used. As chemical vapor standard in ULSI IJ44 high CTEmaterials deposition (CVD), fabs are usually non- spin coating, and PTFEdeposition conductive, a heater evaporation cannot be followedfabricated from a PTFE is a with high conductive material is candidatefor low temperature (above incorporated. A 50 μm dielectric constant350° C.) processing long PTFE bend insulation in ULSI Pigmented inksactuator with Very low power may be infeasible, polysilicon heater andconsumption as pigment particles 15 mW power input Many ink types mayjam the bend can provide 180 μN can be used actuator force and 10 μmSimple planar deflection. Actuator fabrication motions include: Smallchip area Bend required for each Push actuator Buckle Fast operationRotate High efficiency CMOS compatible voltages and currents Easyextension from single nozzles to pagewidth print heads Conductive Apolymer with a high High force can Requires special IJ24 polymercoefficient of thermal be generated materials thermo- expansion (such asVery low power development (High elastic PTFE) is doped with consumptionCTE conductive actuator conducting substances Many ink types polymer) toincrease its can be used Requires a PTFE conductivity to about 3 Simpleplanar deposition process, orders of magnitude fabrication which is notyet below that of copper. Small chip area standard in ULSI Theconducting required for each fabs polymer expands actuator PTFEdeposition when resistively Fast operation cannot be followed heated.High efficiency with high Examples of CMOS temperature (above conductingdopants compatible voltages 350° C.) processing include: and currentsEvaporation and Carbon nanotubes Easy extension CVD deposition Metalfibers from single nozzles techniques cannot Conductive polymers topagewidth print be used such as doped heads Pigmented inks polythiophenemay be infeasible, Carbon granules as pigment particles may jam the bendactuator Shape A shape memory alloy High force is Fatigue limits IJ26memory such as TiNi (also available (stresses maximum number alloy knownas Nitinol - of hundreds of MPa) of cycles Nickel Titanium alloy Largestrain is Low strain (1%) developed at the Naval available (more than isrequired to extend Ordnance Laboratory) 3%) fatigue resistance isthermally switched High corrosion Cycle rate between its weak resistancelimited by heat martensitic state and Simple removal its high stiffnessconstruction Requires unusual austenic state. The Easy extensionmaterials (TiNi) shape of the actuator from single nozzles The latentheat of in its martensitic state to pagewidth print transformation mustis deformed relative to heads be provided the austenic shape. Lowvoltage High current The shape change operation operation causesejection of a Requires pre- drop. stressing to distort the martensiticstate Linear Linear magnetic Linear Magnetic Requires unusual IJ12Magnetic actuators include the actuators can be semiconductor ActuatorLinear Induction constructed with materials such as Actuator (LIA),Linear high thrust, long soft magnetic alloys Permanent Magnet travel,and high (e.g. CoNiFe) Synchronous Actuator efficiency using Somevarieties (LPMSA), Linear planar also require Reluctance semiconductorpermanent magnetic Synchronous Actuator fabrication materials such as(LRSA), Linear techniques Neodymium iron Switched Reluctance Longactuator boron (NdFeB) Actuator (LSRA), and travel is available Requiresthe Linear Stepper Medium force is complex multi- Actuator (LSA).available phase drive circuitry Low voltage High current operationoperation

BASIC OPERATION MODE Description Advantages Disadvantages ExamplesActuator This is the simplest Simple operation Drop repetition Thermalink jet directly mode of operation: the No external rate is usuallyPiezoelectric ink pushes ink actuator directly fields required limitedto around 10 jet supplies sufficient Satellite drops kHz. However, thisIJ01, IJ02, IJ03, kinetic energy to expel can be avoided if is notfundamental IJ04, IJ05, IJ06, the drop. The drop drop velocity is lessto the method, but is IJ07, IJ09, IJ11, must have a sufficient than 4m/s related to the refill IJ12, IJ14, IJ16, velocity to overcome Can beefficient, method normally IJ20, IJ22, IJ23, the surface tension.depending upon the used IJ24, IJ25, IJ26, actuator used All of the dropIJ27, IJ28, IJ29, kinetic energy must IJ30, IJ31, IJ32, be provided bythe IJ33, IJ34, IJ35, actuator IJ36, IJ37, IJ38, Satellite drops IJ39,IJ40, IJ41, usually form if drop IJ42, IJ43, IJ44 velocity is greaterthan 4.5 m/s Proximity The drops to be Very simple print Requires closeSilverbrook, EP printed are selected by head fabrication can proximitybetween 0771 658 A2 and some manner (e.g. be used the print head andrelated patent thermally induced The drop the print media orapplications surface tension selection means transfer roller reductionof does not need to May require two pressurized ink). provide the energyprint heads printing Selected drops are required to separate alternaterows of the separated from the ink the drop from the image in the nozzleby nozzle Monolithic color contact with the print print heads are mediumor a transfer difficult roller. Electro- The drops to be Very simpleprint Requires very Silverbrook, EP static pull printed are selected byhead fabrication can high electrostatic 0771 658 A2 and on ink somemanner (e.g. be used field related patent thermally induced The dropElectrostatic field applications surface tension selection means forsmall nozzle Tone-Jet reduction of does not need to sizes is above airpressurized ink). provide the energy breakdown Selected drops arerequired to separate Electrostatic field separated from the ink the dropfrom the may attract dust in the nozzle by a nozzle strong electricfield. Magnetic The drops to be Very simple print Requires Silverbrook,EP pull on ink printed are selected by head fabrication can magnetic ink0771 658 A2 and some manner (e.g. be used Ink colors other relatedpatent thermally induced The drop than black are applications surfacetension selection means difficult reduction of does not need to Requiresvery pressurized ink). provide the energy high magnetic fields Selecteddrops are required to separate separated from the ink the drop from thein the nozzle by a nozzle strong magnetic field acting on the magneticink. Shutter The actuator moves a High speed (>50 Moving parts are IJ13,IJ17, IJ21 shutter to block ink kHz) operation can required flow to thenozzle. The be achieved due to Requires ink ink pressure is pulsedreduced refill time pressure modulator at a multiple of the Drop timingcan Friction and wear drop ejection be very accurate must be consideredfrequency. The actuator Stiction is energy can be very possible lowShuttered The actuator moves a Actuators with Moving parts are IJ08,IJ15, IJ18, grill shutter to block ink small travel can be required IJ19flow through a grill to used Requires ink the nozzle. The shutterActuators with pressure modulator movement need only small force can beFriction and wear be equal to the width used must be considered of thegrill holes. High speed (>50 Stiction is kHz) operation can possible beachieved Pulsed A pulsed magnetic Extremely low Requires an IJ10magnetic field attracts an ‘ink energy operation is external pulsed pullon ink pusher’ at the drop possible magnetic field pusher ejectionfrequency. An No heat Requires special actuator controls a dissipationmaterials for both catch, which prevents problems the actuator and thethe ink pusher from ink pusher moving when a drop is Complex not to beejected. construction

AUXILIARY MECHANISM (APPLIED TO ALL NOZZLES) Description AdvantagesDisadvantages Examples None The actuator directly Simplicity of Dropejection Most ink jets, fires the ink drop, and construction energy mustbe including there is no external Simplicity of supplied bypiezoelectric and field or other operation individual nozzle thermalbubble. mechanism required. Small physical actuator IJ01, IJ02, IJ03,size IJ04, IJ05, IJ07, IJ09, IJ11, IJ12, IJ14, IJ20, IJ22, IJ23, IJ24,IJ25, IJ26, IJ27, IJ28, IJ29, IJ30, IJ31, IJ32, IJ33, IJ34, IJ35, IJ36,IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44 Oscillating The inkpressure Oscillating ink Requires external Silverbrook, EP ink pressureoscillates, providing pressure can provide ink pressure 0771 658 A2 and(including much of the drop a refill pulse, oscillator related patentacoustic ejection energy. The allowing higher Ink pressure applicationsstimulation) actuator selects which operating speed phase and amplitudeIJ08, IJ13, IJ15, drops are to be fired The actuators must be carefullyIJ17, IJ18, IJ19, by selectively may operate with controlled IJ21blocking or enabling much lower energy Acoustic nozzles. The inkAcoustic lenses reflections in the ink pressure oscillation can be usedto focus chamber must be may be achieved by the sound on the designedfor vibrating the print nozzles head, or preferably by an actuator inthe ink supply. Media The print head is Low power Precision Silverbrook,EP proximity placed in close High accuracy assembly required 0771 658 A2and proximity to the print Simple print head Paper fibers may relatedpatent medium. Selected construction cause problems applications dropsprotrude from Cannot print on the print head further rough substratesthan unselected drops, and contact the print medium. The drop soaks intothe medium fast enough to cause drop separation. Transfer Drops areprinted to a High accuracy Bulky Silverbrook, EP roller transfer rollerinstead Wide range of Expensive 0771 658 A2 and of straight to the printprint substrates can Complex related patent medium. A transfer be usedconstruction applications roller can also be used Ink can be driedTektronix hot for proximity drop on the transfer roller meltpiezoelectric separation. ink jet Any of the IJ series Electro- Anelectric field is Low power Field strength Silverbrook, EP static usedto accelerate Simple print head required for 0771 658 A2 and selecteddrops towards construction separation of small related patent the printmedium. drops is near or applications above air breakdown Tone-JetDirect A magnetic field is Low power Requires Silverbrook, EP magneticused to accelerate Simple print head magnetic ink 0771 658 A2 and fieldselected drops of construction Requires strong related patent magneticink towards magnetic field applications the print medium. Cross Theprint head is Does not require Requires external IJ06, IJ16 magneticplaced in a constant magnetic materials magnet field magnetic field. Theto be integrated in Current densities Lorenz force in a the print headmay be high, current carrying wire manufacturing resulting in is used tomove the process electromigration actuator. problems Pulsed A pulsedmagnetic Very low power Complex print IJ10 magnetic field is used tooperation is possible head construction field cyclically attract a Smallprint head Magnetic paddle, which pushes size materials required in onthe ink. A small print head actuator moves a catch, which selectivelyprevents the paddle from moving.

ACTUATOR AMPLIFICATION OR MODIFICATION METHOD Description AdvantagesDisadvantages Examples None No actuator Operational Many actuatorThermal Bubble mechanical simplicity mechanisms have Ink jetamplification is used. insufficient travel, IJ01, IJ02, IJ06, Theactuator directly or insufficient force, IJ07, IJ16, IJ25, drives thedrop to efficiently drive IJ26 ejection process. the drop ejectionprocess Differential An actuator material Provides greater High stressesare Piezoelectric expansion expands more on one travel in a reducedinvolved IJ03, IJ09, IJ17, bend side than on the other. print head areaCare must be IJ18, IJ19, IJ20, actuator The expansion may be taken thatthe IJ21, IJ22, IJ23, thermal, piezoelectric, materials do not IJ24,IJ27, IJ29, magnetostrictive, or delaminate IJ30, IJ31, IJ32, othermechanism. The Residual bend IJ33, IJ34, IJ35, bend actuator convertsresulting from high IJ36, IJ37, IJ38, a high force low traveltemperature or high IJ39, IJ42, IJ43, actuator mechanism to stressduring IJ44 high travel, lower formation force mechanism. Transient bendA trilayer bend Very good High stresses are IJ40, IJ41 actuator actuatorwhere the two temperature stability involved outside layers are Highspeed, as a Care must be identical. This cancels new drop can be takenthat the bend due to ambient fired before heat materials do nottemperature and dissipates delaminate residual stress. The Cancelsresidual actuator only responds stress of formation to transient heatingof one side or the other. Reverse The actuator loads a Better couplingFabrication IJ05, IJ11 spring spring. When the to the ink complexityactuator is turned off, High stress in the the spring releases. springThis can reverse the force/distance curve of the actuator to make itcompatible with the force/time requirements of the drop ejection.Actuator A series of thin Increased travel Increased Some stackactuators are stacked. Reduced drive fabrication piezoelectric ink jetsThis can be voltage complexity IJ04 appropriate where Increasedactuators require high possibility of short electric field strength,circuits due to such as electrostatic pinholes and piezoelectricactuators. Multiple Multiple smaller Increases the Actuator forces IJ12,IJ13, IJ18, actuators actuators are used force available from may notadd IJ20, IJ22, IJ28, simultaneously to an actuator linearly, reducingIJ42, IJ43 move the ink. Each Multiple efficiency actuator need provideactuators can be only a portion of the positioned to control forcerequired. ink flow accurately Linear A linear spring is used Matches lowRequires print IJ15 Spring to transform a motion travel actuator withhead area for the with small travel and higher travel spring high forceinto a requirements longer travel, lower Non-contact force motion.method of motion transformation Coiled A bend actuator is Increasestravel Generally IJ17, IJ21, IJ34, actuator coiled to provide Reduceschip restricted to planar IJ35 greater travel in a area implementationsreduced chip area. Planar due to extreme implementations are fabricationdifficulty relatively easy to in other orientations. fabricate. FlexureA bend actuator has a Simple means of Care must be IJ10, IJ19, IJ33 bendsmall region near the increasing travel of taken not to exceed actuatorfixture point, which a bend actuator the elastic limit in flexes muchmore the flexure area readily than the Stress remainder of thedistribution is very actuator. The actuator uneven flexing iseffectively Difficult to converted from an accurately model even coilingto an with finite element angular bend, resulting analysis in greatertravel of the actuator tip. Catch The actuator controls a Very lowComplex IJ10 small catch. The catch actuator energy construction eitherenables or Very small Requires external disables movement of actuatorsize force an ink pusher that is Unsuitable for controlled in a bulkpigmented inks manner. Gears Gears can be used to Low force, low Movingparts are IJ13 increase travel at the travel actuators can requiredexpense of duration. be used Several actuator Circular gears, rack Canbe fabricated cycles are required and pinion, ratchets, using standardMore complex and other gearing surface MEMS drive electronics methodscan be used. processes Complex construction Friction, friction, and wearare possible Buckle A buckle plate can be Very fast Must stay within S.Hirata et al, plate used to change a slow movement elastic limits of the“An Ink-jet Head actuator into a fast achievable materials for longUsing Diaphragm motion. It can also device life Microactuator”, converta high force, High stresses Proc. IEEE MEMS, low travel actuatorinvolved February 1996, into a high travel, Generally high pp 418-423.medium force motion. power requirement IJ18, IJ27 Tapered A taperedmagnetic Linearizes the Complex IJ14 magnetic pole can increase magneticconstruction pole travel at the expense force/distance curve of force.Lever A lever and fulcrum is Matches low High stress IJ32, IJ36, IJ37used to transform a travel actuator with around the fulcrum motion withsmall higher travel travel and high force requirements into a motionwith Fulcrum area has longer travel and no linear movement, lower force.The lever and can be used for can also reverse the a fluid sealdirection of travel. Rotary The actuator is High mechanical Complex IJ28impeller connected to a rotary advantage construction impeller. A smallThe ratio of force Unsuitable for angular deflection of to travel of thepigmented inks the actuator results in actuator can be a rotation of thematched to the impeller vanes, which nozzle requirements push the inkagainst by varying the stationary vanes and number of impeller out ofthe nozzle. vanes Acoustic A refractive or No moving parts Large area1993 Hadimioglu lens diffractive (e.g. zone required et al, EUP 550,192plate) acoustic lens is Only relevant for 1993 Elrod et al, used toconcentrate acoustic ink jets EUP 572,220 sound waves. Sharp A sharppoint is used Simple Difficult to Tone-jet conductive to concentrate anconstruction fabricate using point electrostatic field. standard VLSIprocesses for a surface ejecting ink-jet Only relevant for electrostaticink jets

ACTUATOR MOTION Description Advantages Disadvantages Examples Volume Thevolume of the Simple High energy is Hewlett-Packard expansion actuatorchanges, construction in the typically required to Thermal Ink jetpushing the ink in all case of thermal ink achieve volume CanonBubblejet directions. jet expansion. This leads to thermal stress,cavitation, and kogation in thermal ink jet implementations Linear, Theactuator moves in Efficient High fabrication IJ01, IJ02, IJ04, normal toa direction normal to coupling to ink complexity may be IJ07, IJ11, IJ14chip surface the print head surface. drops ejected required to achieveThe nozzle is typically normal to the perpendicular in the line ofsurface motion movement. Parallel to The actuator moves Suitable forFabrication IJ12, IJ13, IJ15, chip surface parallel to the print planarfabrication complexity IJ33, , IJ34, IJ35, head surface. Drop FrictionIJ36 ejection may still be Stiction normal to the surface. Membrane Anactuator with a The effective Fabrication 1982 Howkins push high forcebut small area of the actuator complexity U.S. Pat. No. 4,459,601 areais used to push a becomes the Actuator size stiff membrane that ismembrane area Difficulty of in contact with the ink. integration in aVLSI process Rotary The actuator causes Rotary levers Device IJ05, IJ08,IJ13, the rotation of some may be used to complexity IJ28 element, sucha grill or increase travel May have impeller Small chip area friction ata pivot requirements point Bend The actuator bends A very small Requiresthe 1970 Kyser et al when energized. This change in actuator to be madeU.S. Pat. No. 3,946,398 may be due to dimensions can be from at leasttwo 1973 Stemme differential thermal converted to a large distinctlayers, or to U.S. Pat. No. 3,747,120 expansion, motion. have a thermalIJ03, IJ09, IJ10, piezoelectric difference across the IJ19, IJ23, IJ24,expansion, actuator IJ25, IJ29, IJ30, magnetostriction, or IJ31, IJ33,IJ34, other form of relative IJ35 dimensional change. Swivel Theactuator swivels Allows operation Inefficient IJ06 around a centralpivot. where the net linear coupling to the ink This motion is suitableforce on the paddle motion where there are is zero opposite forces Smallchip area applied to opposite requirements sides of the paddle, e.g.Lorenz force. Straighten The actuator is Can be used with Requirescareful IJ26, IJ32 normally bent, and shape memory balance of stressesstraightens when alloys where the to ensure that the energized. austenicphase is quiescent bend is planar accurate Double The actuator bends inOne actuator can Difficult to make IJ36, IJ37, IJ38 bend one directionwhen be used to power the drops ejected by one element is two nozzles.both bend directions energized, and bends Reduced chip identical. theother way when size. A small another element is Not sensitive toefficiency loss energized. ambient temperature compared to equivalentsingle bend actuators. Shear Energizing the Can increase the Not readily1985 Fishbeck actuator causes a shear effective travel of applicable toother U.S. Pat. No. 4,584,590 motion in the actuator piezoelectricactuator material. actuators mechanisms Radial con- The actuatorsqueezes Relatively easy High force 1970 Zoltan striction an inkreservoir, to fabricate single required U.S. Pat. No. 3,683,212 forcingink from a nozzles from glass Inefficient constricted nozzle. tubing asDifficult to macroscopic integrate with VLSI structures processesCoil/uncoil A coiled actuator Easy to fabricate Difficult to IJ17, IJ21,IJ34, uncoils or coils more as a planar VLSI fabricate for non- IJ35tightly. The motion of process planar devices the free end of the Smallarea Poor out-of-plane actuator ejects the ink. required, thereforestiffness low cost Bow The actuator bows (or Can increase the Maximumtravel IJ16, IJ18, IJ27 buckles) in the middle speed of travel isconstrained when energized. Mechanically High force rigid requiredPush-Pull Two actuators control The structure is Not readily IJ18 ashutter. One actuator pinned at both ends, suitable for ink jets pullsthe shutter, and so has a high out-of- which directly push the otherpushes it. plane rigidity the ink Curl A set of actuators curl Goodfluid flow Design IJ20, IJ42 inwards inwards to reduce the to the regionbehind complexity volume of ink that the actuator they enclose.increases efficiency Curl A set of actuators curl Relatively simpleRelatively large IJ43 outwards outwards, pressurizing construction chiparea ink in a chamber surrounding the actuators, and expelling ink froma nozzle in the chamber. Iris Multiple vanes enclose High efficiencyHigh fabrication IJ22 a volume of ink. These Small chip area complexitysimultaneously rotate, Not suitable for reducing the volume pigmentedinks between the vanes. Acoustic The actuator vibrates The actuator canLarge area 1993 Hadimioglu vibration at a high frequency. be physicallydistant required for et al, EUP 550,192 from the ink efficient operation1993 Elrod et al, at useful frequencies EUP 572,220 Acoustic couplingand crosstalk Complex drive circuitry Poor control of drop volume andposition None In various ink jet No moving parts Various otherSilverbrook, EP designs the actuator tradeoffs are 0771 658 A2 and doesnot move. required to related patent eliminate moving applications partsTone-jet

NOZZLE REFILL METHOD Description Advantages Disadvantages ExamplesSurface This is the normal way Fabrication Low speed Thermal ink jettension that ink jets are simplicity Surface tension Piezoelectric inkrefilled. After the Operational force relatively jet actuator isenergized, simplicity small compared to IJ01-IJ07, IJ10-IJ14, ittypically returns actuator force IJ16, IJ20, IJ22-IJ45 rapidly to itsnormal Long refill time position. This rapid usually dominates returnsucks in air the total repetition through the nozzle rate opening. Theink surface tension at the nozzle then exerts a small force restoringthe meniscus to a minimum area. This force refills the nozzle. ShutteredInk to the nozzle High speed Requires IJ08, IJ13, IJ15, oscillatingchamber is provided at Low actuator common ink IJ17, IJ18, IJ19, inkpressure a pressure that energy, as the pressure oscillator IJ21oscillates at twice the actuator need only May not be drop ejection openor close the suitable for frequency. When a shutter, instead ofpigmented inks drop is to be ejected, ejecting the ink the shutter isopened drop for 3 half cycles: drop ejection, actuator return, andrefill. The shutter is then closed to prevent the nozzle chamberemptying during the next negative pressure cycle. Refill After the mainHigh speed, as Requires two IJ09 actuator actuator has ejected a thenozzle is independent drop a second (refill) actively refilled actuatorsper nozzle actuator is energized. The refill actuator pushes ink intothe nozzle chamber. The refill actuator returns slowly, to prevent itsreturn from emptying the chamber again. Positive ink The ink is held aslight High refill rate, Surface spill Silverbrook, EP pressure positivepressure. therefore a high must be prevented 0771 658 A2 and After theink drop is drop repetition rate Highly related patent ejected, thenozzle is possible hydrophobic print applications chamber fills quicklyhead surfaces are Alternative for:, as surface tension and requiredIJ01-IJ07, IJ10-IJ14, ink pressure both IJ16, IJ20, IJ22-IJ45 operate torefill the nozzle.

METHOD OF RESTRICTING BACK-FLOW THROUGH INLET Description AdvantagesDisadvantages Examples Long inlet The ink inlet channel Designsimplicity Restricts refill Thermal ink jet channel to the nozzlechamber Operational rate Piezoelectric ink is made long and simplicityMay result in a jet relatively narrow, Reduces relatively large chipIJ42, IJ43 relying on viscous crosstalk area drag to reduce inlet Onlypartially back-flow. effective Positive ink The ink is under a Dropselection Requires a Silverbrook, EP pressure positive pressure, so andseparation method (such as a 0771 658 A2 and that in the quiescentforces can be nozzle rim or related patent state some of the ink reducedeffective applications drop already protrudes Fast refill timehydrophobizing, or Possible from the nozzle. both) to prevent operationof the This reduces the flooding of the following: IJ01-IJ07, pressurein the nozzle ejection surface of IJ09-IJ12, IJ14, chamber which is theprint head. IJ16, IJ20, IJ22, required to eject a IJ23-IJ34, certainvolume of ink. IJ36-IJ41, IJ44 The reduction in chamber pressure resultsin a reduction in ink pushed out through the inlet. Baffle One or morebaffles The refill rate is Design HP Thermal Ink are placed in the inletnot as restricted as complexity Jet ink flow. When the the long inletMay increase Tektronix actuator is energized, method. fabricationpiezoelectric ink the rapid ink Reduces complexity (e.g. jet movementcreates crosstalk Tektronix hot melt eddies which restrict Piezoelectricprint the flow through the heads). inlet. The slower refill process isunrestricted, and does not result in eddies. Flexible flap In thismethod recently Significantly Not applicable to Canon restrictsdisclosed by Canon, reduces back-flow most ink jet inlet the expandingactuator for edge-shooter configurations (bubble) pushes on a thermalink jet Increased flexible flap that devices fabrication restricts theinlet. complexity Inelastic deformation of polymer flap results in creepover extended use Inlet filter A filter is located Additional Restrictsrefill IJ04, IJ12, IJ24, between the ink inlet advantage of ink rateIJ27, IJ29, IJ30 and the nozzle filtration May result in chamber. Thefilter Ink filter may be complex has a multitude of fabricated with noconstruction small holes or slots, additional process restricting inkflow. steps The filter also removes particles which may block thenozzle. Small inlet The ink inlet channel Design simplicity Restrictsrefill IJ02, IJ37, IJ44 compared to the nozzle chamber rate to nozzlehas a substantially May result in a smaller cross section relativelylarge chip than that of the nozzle, area resulting in easier ink Onlypartially egress out of the effective nozzle than out of the inlet.Inlet shutter A secondary actuator Increases speed Requires separateIJ09 controls the position of of the ink-jet print refill actuator and ashutter, closing off head operation drive circuit the ink inlet when themain actuator is energized. The inlet is The method avoids the Back-flowRequires careful IJ01, IJ03, 1J05, located problem of inlet back-problem is design to minimize IJ06, IJ07, IJ10, behind the flow byarranging the eliminated the negative IJ11, IJ14, IJ16, ink-pushingink-pushing surface of pressure behind the IJ22, IJ23, IJ25, surface theactuator between paddle IJ28, IJ31, IJ32, the inlet and the IJ33, IJ34,IJ35, nozzle. IJ36, IJ39, IJ40, IJ41 Part of the The actuator and aSignificant Small increase in IJ07, IJ20, IJ26, actuator wall of the inkreductions in fabrication IJ38 moves to chamber are arranged back-flowcan be complexity shut off the so that the motion of achieved inlet theactuator closes off Compact designs the inlet. possible Nozzle In someconfigurations Ink back-flow None related to Silverbrook, EP actuator ofink jet, there is no problem is ink back-flow on 0771 658 A2 and doesnot expansion or eliminated actuation related patent result in inkmovement of an applications back-flow actuator which may Valve-jet causeink back-flow Tone-jet through the inlet.

NOZZLE CLEARING METHOD Description Advantages Disadvantages ExamplesNormal All of the nozzles are No added May not be Most ink jet nozzlefiring fired periodically, complexity on the sufficient to systemsbefore the ink has a print head displace dried ink IJ01, IJ02, IJ03,chance to dry. When IJ04, IJ05, IJ06, not in use the nozzles IJ07, IJ09,IJ10, are sealed (capped) IJ11, IJ12, IJ14, against air. IJ16, IJ20,IJ22, The nozzle firing is IJ23, IJ24, IJ25, usually performed IJ26,IJ27, IJ28, during a special IJ29, IJ30, IJ31, clearing cycle, afterIJ32, IJ33, IJ34, first moving the print IJ36, IJ37, IJ38, head to acleaning IJ39, IJ40,, IJ41, station. IJ42, IJ43, IJ44,, IJ45 Extra Insystems which heat Can be highly Requires higher Silverbrook, EP powerto the ink, but do not boil effective if the drive voltage for 0771 658A2 and ink heater it under normal heater is adjacent to clearing relatedpatent situations, nozzle the nozzle May require applications clearingcan be larger drive achieved by over- transistors powering the heaterand boiling ink at the nozzle. Rapid The actuator is fired in Does notrequire Effectiveness May be used succession rapid succession. In extradrive circuits depends with: IJ01, IJ02, of actuator someconfigurations, on the print head substantially upon IJ03, IJ04, IJ05,pulses this may cause heat Can be readily the configuration of IJ06,IJ07, IJ09, build-up at the nozzle controlled and the ink jet nozzleIJ10, IJ11, IJ14, which boils the ink, initiated by digital IJ16, IJ20,IJ22, clearing the nozzle. In logic IJ23, IJ24, IJ25, other situations,it may IJ27, IJ28, IJ29, cause sufficient IJ30, IJ31, IJ32, vibrationsto dislodge IJ33, IJ34, IJ36, clogged nozzles. IJ37, IJ38, IJ39, IJ40,IJ41, IJ42, IJ43, IJ44, IJ45 Extra Where an actuator is A simple Notsuitable May be used power to not normally driven to solution wherewhere there is a with: IJ03, IJ09, ink pushing the limit of its motion,applicable hard limit to IJ16, IJ20, IJ23, actuator nozzle clearing maybe actuator movement IJ24, IJ25, IJ27, assisted by providing IJ29, IJ30,IJ31, an enhanced drive IJ32, IJ39, IJ40, signal to the actuator. IJ41,IJ42, IJ43, IJ44, IJ45 Acoustic An ultrasonic wave is A high nozzle HighIJ08, IJ13, IJ15, resonance applied to the ink clearing capabilityimplementation cost IJ17, IJ18, IJ19, chamber. This wave is can beachieved if system does not IJ21 of an appropriate May be alreadyinclude an amplitude and implemented at very acoustic actuator frequencyto cause low cost in systems sufficient force at the which alreadynozzle to clear include acoustic blockages. This is actuators easiest toachieve if the ultrasonic wave is at a resonant frequency of the inkcavity. Nozzle A microfabricated Can clear Accurate Silverbrook, EPclearing plate is pushed against severely clogged mechanical 0771 658 A2and plate the nozzles. The plate nozzles alignment is related patent hasa post for every required applications nozzle. A post moves Moving partsare through each nozzle, required displacing dried ink. There is risk ofdamage to the nozzles Accurate fabrication is required Ink The pressureof the ink May be effective Requires May be used pressure is temporarilywhere other pressure pump or with all IJ series ink pulse increased sothat ink methods cannot be other pressure jets streams from all of theused actuator nozzles. This may be Expensive used in conjunctionWasteful of ink with actuator energizing. Print head A flexible ‘blade’is Effective for Difficult to use if Many ink jet wiper wiped across theprint planar print head print head surface is systems head surface. Thesurfaces non-planar or very blade is usually Low cost fragile fabricatedfrom a Requires flexible polymer, e.g. mechanical parts rubber orsynthetic Blade can wear elastomer. out in high volume print systemsSeparate A separate heater is Can be effective Fabrication Can be usedwith ink boiling provided at the nozzle where other nozzle complexitymany IJ series ink heater although the normal clearing methods jets drope-ection cannot be used mechanism does not Can be require it. Theheaters implemented at no do not require additional cost in individualdrive some ink jet circuits, as many configurations nozzles can becleared simultaneously, and no imaging is required.

NOZZLE PLATE CONSTRUCTION Description Advantages Disadvantages ExamplesElectro- A nozzle plate is Fabrication High Hewlett Packard formedseparately fabricated simplicity temperatures and Thermal Ink jet nickelfrom electroformed pressures are nickel, and bonded to required to bondthe print head chip. nozzle plate Minimum thickness constraintsDifferential thermal expansion Laser Individual nozzle No masks Eachhole must Canon Bubblejet ablated or holes are ablated by an required beindividually 1988 Sercel et drilled intense UV laser in a Can be quitefast formed al., SPIE, Vol. 998 polymer nozzle plate, which is Somecontrol Special Excimer Beam typically a polymer over nozzle profileequipment required Applications, pp. such as polyimide or is possibleSlow where there 76-83 polysulphone Equipment are many thousands 1993Watanabe required is relatively of nozzles per print et al., U.S. Pat.No. low cost head 5,208,604 May produce thin burrs at exit holes SiliconA separate nozzle High accuracy is Two part K. Bean, IEEE micro- plateis attainable construction Transactions on machined micromachined fromHigh cost Electron Devices, single crystal silicon, Requires Vol. ED-25,No. 10, and bonded to the precision alignment 1978, pp 1185-1195 printhead wafer. Nozzles may be Xerox 1990 clogged by adhesive Hawkins etal., U.S. Pat. No. 4,899,181 Glass Fine glass capillaries No expensiveVery small 1970 Zoltan capillaries are drawn from glass equipmentrequired nozzle sizes are U.S. Pat. No. 3,683,212 tubing. This methodSimple to make difficult to form has been used for single nozzles Notsuited for making individual mass production nozzles, but is difficultto use for bulk manufacturing of print heads with thousands of nozzles.Monolithic, The nozzle plate is High accuracy Requires Silverbrook, EPsurface deposited as a layer (<1 μm) sacrificial layer 0771 658 A2 andmicro- using standard VLSI Monolithic under the nozzle related patentmachined deposition techniques. Low cost plate to form the applicationsusing VLSI Nozzles are etched in Existing nozzle chamber IJ01, IJ02,IJ04, litho- the nozzle plate using processes can be Surface may beIJ11, IJ12, IJ17, graphic VLSI lithography and used fragile to the touchIJ18, IJ20, IJ22, processes etching. IJ24, IJ27, IJ28, IJ29, IJ30, IJ31,IJ32, IJ33, IJ34, IJ36, IJ37, IJ38, IJ39, IJ40, IJ41, IJ42, IJ43, IJ44Monolithic, The nozzle plate is a High accuracy Requires long IJ03,IJ05, IJ06, etched buried etch stop in the (<1 μm) etch times IJ07,IJ08, IJ09, through wafer. Nozzle Monolithic Requires a IJ10, IJ13,IJ14, substrate chambers are etched in Low cost support wafer IJ15,IJ16, IJ19, the front of the wafer, No differential IJ21, IJ23, IJ25,and the wafer is expansion IJ26 thinned from the back side. Nozzles arethen etched in the etch stop layer. No nozzle Various methods have Nonozzles to Difficult to Ricoh 1995 plate been tried to eliminate becomeclogged control drop Sekiya et al the nozzles entirely, to positionaccurately U.S. Pat. No. 5,412,413 prevent nozzle Crosstalk 1993Hadimioglu clogging. These problems et al EUP 550,192 include thermalbubble 1993 Elrod et al mechanisms and EUP 572,220 acoustic lensmechanisms Trough Each drop ejector has Reduced Drop firing IJ35 atrough through manufacturing direction is sensitive which a paddlemoves. complexity to wicking. There is no nozzle Monolithic plate.Nozzle slit The elimination of No nozzles to Difficult to 1989 Saito etal instead of nozzle holes and become clogged control drop U.S. Pat. No.4,799,068 individual replacement by a slit position accurately nozzlesencompassing many Crosstalk actuator positions problems reduces nozzleclogging, but increases crosstalk due to ink surface waves

DROP EJECTION DIRECTION Description Advantages Disadvantages ExamplesEdge Ink flow is along the Simple Nozzles limited Canon Bubblejet (‘edgesurface of the chip, construction to edge 1979 Endo et al GB shooter’)and ink drops are No silicon High resolution patent 2,007,162 ejectedfrom the chip etching required is difficult Xerox heater-in- edge. Goodheat Fast color pit 1990 Hawkins et al sinking via substrate printingrequires U.S. Pat. No. 4,899,181 Mechanically one print head perTone-jet strong color Ease of chip handing Surface Ink flow is along theNo bulk silicon Maximum ink Hewlett-Packard (‘roof surface of the chip,etching required flow is severely TIJ 1982 Vaught et al shooter’) andink drops are Silicon can make restricted U.S. Pat. No. 4,490,728ejected from the chip an effective heat IJ02, IJ11, IJ12, surface,normal to the sink IJ20, IJ22 plane of the chip. Mechanical strengthThrough Ink flow is through the High ink flow Requires bulk Silverbrook,EP chip, chip, and ink drops are Suitable for silicon etching 0771 658A2 and forward ejected from the front pagewidth print related patent(‘up surface of the chip. heads applications shooter’) High nozzle IJ04,IJ17, IJ18, packing density IJ24, IJ27-IJ45 therefore low manufacturingcost Through Ink flow is through the High ink flow Requires wafer IJ01,IJ03, IJ05, chip, chip, and ink drops are Suitable for thinning IJ06,IJ07, IJ08, reverse ejected from the rear pagewidth print Requiresspecial IJ09, IJ10, IJ13, (‘down surface of the chip. heads handlingduring IJ14, IJ15, IJ16, shooter’) High nozzle manufacture IJ19, IJ21,IJ23, packing density IJ25, IJ26 therefore low manufacturing costThrough Ink flow is through the Suitable for Pagewidth print EpsonStylus actuator actuator, which is not piezoelectric print heads requireTektronix hot fabricated as part of heads several thousand meltpiezoelectric the same substrate as connections to drive ink jets thedrive transistors. circuits Cannot be manufactured in standard CMOS fabsComplex assembly required

INK TYPE Description Advantages Disadvantages Examples Aqueous, Waterbased ink which Environmentally Slow drying Most existing ink dyetypically contains: friendly Corrosive jets water, dye, surfactant, Noodor Bleeds on paper All IJ series ink humectant, and May jets biocide.strikethrough Silverbrook, EP Modern ink dyes have Cockles paper 0771658 A2 and high water-fastness, related patent light fastnessapplications Aqueous, Water based ink which Environmentally Slow dryingIJ02, IJ04, IJ21, pigment typically contains: friendly Corrosive IJ26,IJ27, IJ30 water, pigment, No odor Pigment may Silverbrook, EPsurfactant, humectant, Reduced bleed clog nozzles 0771 658 A2 and andbiocide. Reduced wicking Pigment may related patent Pigments have anReduced clog actuator applications advantage in reduced strikethroughmechanisms Piezoelectric ink- bleed, wicking and Cockles paper jetsstrikethrough. Thermal ink jets (with significant restrictions) MethylMEK is a highly Very fast drying Odorous All IJ series ink Ethylvolatile solvent used Prints on various Flammable jets Ketone forindustrial printing substrates such as (MEK) on difficult surfacesmetals and plastics such as aluminum cans. Alcohol Alcohol based inksFast drying Slight odor All IJ series ink (ethanol, can be used wherethe Operates at sub- Flammable jets 2-butanol, printer must operate atfreezing and others) temperatures below temperatures the freezing pointof Reduced paper water. An example of cockle this is in-camera Low costconsumer photographic printing. Phase The ink is solid at No dryingtime- High viscosity Tektronix hot change room temperature, and inkinstantly freezes Printed ink melt piezoelectric (hot melt) is melted inthe print on the print medium typically has a ink jets head beforejetting. Almost any print ‘waxy’ feel 1989 Nowak Hot melt inks aremedium can be used Printed pages U.S. Pat. No. usually wax based, Nopaper cockle may ‘block’ 4,820,346 with a melting point occurs Inktemperature All IJ series ink around 80° C. After No wicking may beabove the jets jetting the ink freezes occurs curie point of almostinstantly upon No bleed occurs permanent magnets contacting the print Nostrikethrough Ink heaters medium or a transfer occurs consume powerroller. Long warm-up time Oil Oil based inks are High solubility Highviscosity: All IJ series ink extensively used in medium for some this isa significant jets offset printing. They dyes limitation for use in haveadvantages in Does not cockle ink jets, which improved paper usuallyrequire a characteristics on Does not wick low viscosity. Some paper(especially no through paper short chain and wicking or cockle).multi-branched oils Oil soluble dies and have a sufficiently pigmentsare required. low viscosity. Slow drying Micro- A microemulsion is aStops ink bleed Viscosity higher All IJ series ink emulsion stable, selfforming High dye than water jets emulsion of oil, water, solubility Costis slightly and surfactant. The Water, oil, and higher than watercharacteristic drop size amphiphilic soluble based ink is less than 100nm, dies can be used High surfactant and is determined by Can stabilizeconcentration the preferred curvature pigment required (around of thesurfactant. suspensions 5%)

1. An inkjet printhead comprising: a plurality of nozzles formed on asubstrate; at least one nozzle plate spaced apart from the substrate;and a plurality of walls extending between the nozzle plate and thesubstrate, wherein the at least one nozzle plate is supported, at leastpartially, by photoresist encapsulated by at least said walls.
 2. Theinkjet printhead of claim 1, wherein each nozzle comprises: a nozzlechamber having a nozzle aperture; and an actuator for ejecting inkthrough the nozzle aperture.
 3. The inkjet printhead of claim 2, whereineach nozzle comprises a bubble-forming heater element actuator suspendedin the nozzle chamber.
 4. The inkjet printhead of claim 2, wherein eachnozzle chamber comprises a roof, which forms at least a part of thenozzle plate.
 5. The inkjet printhead of claim 4, wherein the nozzleaperture is defined in the roof.
 6. The inkjet printhead of claim 4,wherein chamber sidewall extend from the nozzle plate to the substrate.7. The inkjet printhead of claim 4, wherein support walls extend fromthe nozzle plate to the substrate, the support walls being positionedoutside the nozzle chamber.
 8. The inkjet printhead of claim 7, whereinthe photoresist is encapsulated in a volume defined by at least part ofthe substrate, the chamber sidewalls, the support walls and the nozzleplate.
 9. The inkjet printhead of claim 1, wherein the nozzle plate andthe walls are comprised of any one of; silicon nitride, silicon oxide orsilicon oxynitride.
 10. The inkjet printhead of claim 1, wherein thenozzle plate is formed by plasma-enhanced chemical vapour depositiononto a sacrificial photoresist scaffold.
 11. The inkjet printhead ofclaim 10, wherein at least part of the sacrificial photoresist scaffoldis encapsulated by the plasma-enhanced chemical vapour deposition. 12.The inkjet printhead of claim 1, wherein the encapsulated photoresist isresistant to ashing by virtue of its encapsulation.
 13. The inkjetprinthead of claim 1, which is a pagewidth printhead.
 14. The inkjetprinthead of claim 1 having a nozzle density sufficient to print animage at up to 1600 dpi.
 15. A printer comprising the inkjet printheadof claim
 1. 16. A printhead integrated circuit, suitable for forming atleast part of a pagewidth inkjet printhead, the printhead integratedcircuit comprising: a plurality of nozzles formed on a substrate; atleast one nozzle plate spaced apart from the substrate; and, a pluralityof walls extending between the nozzle plate and the substrate whereinthe at least one nozzle plate is supported, at least partially, byphotoresist encapsulated by at least said walls, and wherein said wailsand said nozzle plate are comprised of any one of the group comprisingsilicon nitride, silicon oxide and silicon oxynitride.